A valvetrain assembly is commonly known and used in combustion engines to ensure that the valves are opened and closed in synchronization with the movement of the pistons in the cylinders.
The timing and lift of the valves is determined by the profile of the cam corresponding to the specific valve. However, the profile is static and cannot be changed, so the profile is a compromise between for example fuel consumption, power and emissions.
It is further known in the prior art to provide a variable valve actuation to change the timing and lift of the valves while running the engine. Numerous techniques are used to achieve this.
One technique is providing two differently shaped cams on the cam shaft for each valve and shifting the camshaft axially while running the engine. This allows one to use two different valve timing profiles. For example, one profile to have high power, but also high fuel consumption and emissions, and the other profile for less power, but better fuel consumption and lower emission.
Another technique is to change the phase of the camshaft, such that the lifting of the valves is advanced or delayed. By for example delaying the closing of the exhaust valve, will ensure that more burned fuel is driven out of the cylinder, such that more fuel can be burned in the next stroke.
Also electro-hydraulic systems are used in which a body is arranged between the cam and the valve, which can either transmit the actuation by the cam or absorb the actuation. To this end, the body is telescopic and filled with hydraulic fluid. When a drain opening is closed by an electric valve, the body is stiff and cannot collapse and the valve is actuated by the cam. However, when the drain opening is opened, the hydraulic fluid can be pushed out and the body can be compressed, such that the actuation of the cam is absorbed and the valve stays in a closed position.
Now by electronically controlling the electric valve one can change the profile of the cam and therefor the timing and lift of the valve. If the full profile of the cam is to be used, the valve remains closed, but if only part of the valve lift is desired, the electric valve is opened during the actuation of the valve by the cam.
However, the temperature, the pressure and the viscosity of the hydraulic oil influences the characteristics of electro-hydraulic variable valve actuation.
It is furthermore known to operate the valves without the use of cams, for example by a solenoid type of actuation system. However, such systems are complex and with high costs, as such an actuator is needed for each valve of a combustion engine.